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Dermatome (anatomy)
A dermatome is an area of skin that is mainly supplied by a single spinal nerve. There are eight cervical nerves (C1 being an exception with no dermatome), twelve thoracic nerves, five lumbar nerves and five sacral nerves. Each of these nerves relays sensation (including pain) from a particular region of skin to the brain. Along the thorax and abdomen the dermatomes are like a stack of discs forming a human, each supplied by a different spinal nerve. Along the arms and the legs, the pattern is different: the dermatomes run longitudinally along the limbs. Although the general pattern is similar in all people, the precise areas of innervation are as unique to an individual as fingerprints. A similar area innervated by peripheral nerves is called a peripheral nerve field. Clinical significance A dermatome is an area of skin supplied by sensory neurons that arise from a spinal nerve ganglion. Symptoms that follow a dermatome (e.g. like pain or a rash) may indicate a pathology that involves the related nerve root. Examples include somatic dysfunction of the spine or viral infection. Referred pain usually involves a specific, "referred" location so is not associated with a dermatome. Viruses that hibernate in nerve ganglia (e.g. Varicella zoster virus, which causes both chickenpox and herpes zoster) often cause either pain, rash or both in a pattern defined by a dermatome. However, the symptoms may not appear across the entire dermatome. Important dermatomes and anatomical landmarks Following is a list of spinal nerves and points that are characteristically belonging to the dermatome of each nerve:Key Sensory Points from International Standards for the Classification of Spinal Cord Injury. June 200 * C2 - At least one cm lateral to the occipital protuberance at the base of the skull. Alternately, a point at least 3 cm behind the ear. * C3 - In the supraclavicular fossa, at the midclavicular line. * C4 - Over the acromioclavicular joint. * C5 - On the lateral (radial) side of the antecubital fossa, just proximally to the elbow. * C6 - On the dorsal surface of the proximal phalanx of the thumb. * C7 - On the dorsal surface of the proximal phalanx of the middle finger. * C8 - On the dorsal surface of the proximal phalanx of the little finger. * T1 - On the medial (ulnar) side of the antecubital fossa, just proximally to the medial epicondyle of the humerus. * T2 - At the apex of the axilla. * T3 - Intersection of the midclavicular line and the third intercostal space * T4 - Intersection of the midclavicular line and the fourth intercostal space, located at the level of the nipples. * T5 - Intersection of the midclavicular line and the fifth intercostal space, horizontally located midway between the level of the nipples and the level of the xiphoid process. * T6 - Intersection of the midclavicular line and the horizonal level of the xiphoid process. * T7 - Intersection of the midclavicular line and the horizontal level at one quarter the distance between the level of the xiphoid process and the level of the umbilicus. * T8 - Intersection of the midclavicular line and the horizontal level at one half the distance between the level of the xiphoid process and the level of the umbilicus. * T9 - Intersection of the midclavicular line and the horizontal level at three quarters of the distance between the level of the xiphoid process and the level of the umbilicus. * T10 - Intersection of the midclavicular line, at the horizontal level of the umbilicus. * T11 - Intersection of the midclavicular line, at the horizontal level midway between the level of the umbilicus and the inguinal ligament. * T12 - Intersection of the midclavicular line and the midpoint of the inguinal ligament. * L1 - Midway between the key sensory points for T12 and L2. * L2 - On the anterior medial thigh, at the midpoint of a line connecting the midpoint of the inguinal ligament and the medial epicondyle of the femur. * L3 - At the medial epicondyle of the femur. * L4 - Over the medial malleolus. * L5 - On the dorsum of the foot at the third metatarsophalangeal joint. *S1 - On the lateral aspect of the calcaneus. *S2 - At the midpoint of the popliteal fossa. *S3 - Over the tuberosity of the ischium or infragluteal fold *S4 and S5 - In the perianal area, less than one cm lateral to the mucocutaneous zone Additional images Image:Gray811and813.PNG|Cutaneous nerves of right upper extremity. Image:Gray812and814.PNG|Diagram of segmental distribution of the cutaneous nerves of the right upper extremity. Image:Gray826and831.PNG|Lower limb. Image:Gray834.svg|Foot. See also * Cutaneous innervation * Cutaneous receptive field * Peripheral nerve field * Dorsal root References External links * 3D Dermatomes Web App, Instamedic * * Diagram "Adult Dermatome", The New York Times Category:Somatic sensory system Category:Neurology Category:Skin anatomy